Rekha K, Vaiyapuri Anandh, Pavithra D, Vijayaraghavan R, Manoj Abraham M, and Samuel Sundar Doss D. “Efficacy of the Flutter Therapy in Airway Clearance”. International Journal of Research in Pharmaceutical Sciences, vol. 9, no. 3, Sept. 2018, pp. 917-25, https://ijrps.com/home/article/view/4373.